Direct current (DC) voltage distribution systems have become more common in the past few years. Automobiles operate on 12 volts, sometimes 6 volts DC. Some large scale power distribution in the former Soviet Union is through transmission of DC voltages. While there are certain inefficiencies associated with distributing DC voltages, one of the more significant difficulties is converting the distribution voltage into a usable application voltage. A distribution or system operating voltage of 12 volts, as in an automobile, may be unusable to power a particular appliance which may require a larger or smaller voltage, or both, to power it. Similarly, a system voltage distribution of several hundred or thousand volts may be practical for the distribution system, but may be inappropriate to power the particular appliances desired.
Attempts to solve power transmission problems and achieve greater efficiency include U.S. Pat. No. 4,751,398 issued to Ertz. Ertz describes a lighting system which converts 2 or 3 phase alternating current input to a direct current output. The direct current output is then distributed to several fluorescent lamp ballasts, which in turn drive fluorescent lamps. In addition, a battery backup system provides a DC power source to the fluorescent lamp ballasts in the event of AC power failure. While the AC power is operating, a battery charger maintains the power level of the battery.
U.S. Pat. No. 4,719,550 issued to Powell discloses a power conversion system dedicated to providing an uninterruptable power supply.
U.S. Pat. No. 4,590,546 issued to Maile discloses a circuit for providing a regulated DC voltage output from a wide range of AC inputs. The circuit relies on a voltage doubler to boost a low AC input level, and a full wave rectifier when the AC voltage is higher.
U.S. Pat. No. 4,538,073 issued to Freige discloses a power distribution system for use in desk top computers. The system provides a DC voltage to a number of remote modules which then regulate the voltage down to the required voltage level. Each of the remote modules are preselected for either 5 volt or 12 volt operation. All of the remote modules are driven by a common 33 kHz signal generator to force all of the remote modules to operate in unison and prevent feedback.
U.S. Pat. No. 4,961,130 issued to Kirchberg describes a pulse width modulation invertor which is intended to accommodate harmonic distortion through the use of "quick" or fast fourier transforms.